Solaris Tunable Parameters Reference Manual



Controls the behavior of the NFS version 2 server when it processes WRITE requests. The NFS version 2 protocol mandates that all modified data and metadata associated with the WRITE request reside on stable storage before the server can respond to the client. NFS version 2 WRITE requests are limited to 8192 bytes of data. Thus, each WRITE request might cause multiple small writes to the storage subsystem. This can cause a performance problem.

One trick to accelerate NFS version 2 WRITEs is to take advantage of a client behavior. Clients tend to send out WRITE requests in batches. The server can take advantage of this behavior by clustering together the different WRITE requests into a single request to the underlying file system. Thus, the data to be written to the storage subsystem can be written in fewer, larger requests. This can increase the throughput for WRITE requests tremendously.

Data Type

Integer (32–bit)


1 (clustering enabled)


0 (clustering disabled), 1 (clustering enabled)


Boolean values





When to Change

Some very small NFS clients, particularly PC clients, might not batch WRITE requests. Thus, the behavior required from the clients might not exist, and the clustering in the NFS version 2 server might just add overhead and slow down performance instead of increasing it.

Stability Level